Electric fuse and contact therefor



Aug. 27, 1940. M. B. WOOD 2,213,032

ELECTRIC FUSE AND CONTACT THEREFOR Filed Sept. 30. 1937 fi'evereior k W m urn-17 Patented Aug. 27, 1940 UNlTED STATES ELECTRIC FUSE AND CONTACT THEREFOR Morris B. Wood, Newburyport, Mass, assignor to The Chase-Shawmut Company, Newburyport, Mass, a corporation of Massachusetts Application September 30, 1937, Serial No. 166,545

1 Claim.

This invention relates to electic fuses and particularly those of the plug type and having a center contact. The invention more especially relates to an improved form of center contact and 5 to a plug construction by which the contact can be secured to the plug.

In the usual form of plug type fuse, where the plug body is made of ceramic material, such as porcelain, and has a link containing chamber 10 that is open at the top and is covered by a cap, the center contact is ordinarily in the form of a rivet which is extended through a molded hole in the bottom wall of the body and is headed over inside the link chamber. This type of center con- 15 tact is also usual in plug fuses where the plug body is made of glass having an open bottom link chamber closed by a molded disc or bushing of artificial resin or other molding compound that carries the center contact.

20 In such a plug the contact carrying bottom wall is necessarily of variable thickness due to the characteristics of the molding process. When thecenter contact is in rivet form, the riveting dies are set to come together a predetermined thickness which cannot be varied commercially from plug to plug. Hence some plugs with thin walls have loose contacts thereon and other plugs, with thick walls, have the walls cracked or chipped.

I have discovered that better form of center contact can be advantageously employed in connection with the last described type of fuse, or one wherein the bottom wall of the body is composed at least in part of molded or indentablematerial, such as an artificial resin, fibre and the like, that is cheaper than the rivet form of contact and can be fixed in the fuse body more cheaply and quicker and will stay in position better and be securely non-rotatably fixed to the body. The combination of a fuse having a center contact provided with such characteristics constitutes an object of the present invention.

The fuse of the present invention comprises a 45 body which has a Wall composed at least in part of some material such as an artificial resin, fibre or the usual molding compounds, which is capable of being cut or indented by a screw thread, and a center contact comprising a shank provided with 50 one or more outstanding cutting ribs or projections, as, for instance, long pitch cutting threads and driven into a hole through the wall, the hole being smaller in diameter than the diameter across the ribs so that the ribs bite into the ma- 55 terial of the wall and firmly hold the center contact in position. Such a fuse constitutes a further object of the invention.

Another object of the invention is generally to improve the construction of electric fuses.

Fig. 1 is a vertical section through a plug type fuse embodying the present invention.

Fig. 2 is a longitudinal section through the center contact carrying member of Fig. 1.

Fig. 3 is a view of the center contact.

Fig. 4 is a section taken along line 44 of Fig. l.

Fig. 5 is a view of a modified form of center contact provided with axial instead of spiral ribs.

Fig. 6 is a section taken along line 65 of Fig. 5.

The fuse embodying the present invention comprises a plug body or casing It] made of a molded material, for instance, glass, having a link containing chamber [2 which is open at the bottom and closed at the top by a window it which, for a glass body, is integral with the body. The periphery of the body is provided with screw-threads it which receive an exterior-1y and interiorly screw-threaded metal terminal shell IS. The open bottom end of the body is closed by a plug or bushing 20 which constitutes the bottom wall of the plug body and has an outstanding annular flange 22 which is seated upon the bottom edge of the plug body. The terminal shell i8 has an inturned annular flange 24 which underlies the flange 22 and secures the bushing to the plug body. A fusible link 26 has one end extended 30 through a slot 28 in the flange 22 and secured to the inner face of the shell flange 24 by solder 30. The other end of the fusible link is secured to the inner end of the center contact member 32.

The center contact member comprises a head 34 which overlies the bottom face of the bushing 20 and provides a bottom contact face. A preferably long shank 36 rises from the head 34 and in the form shown in Figs. 1, 2, and 3, is provided with a long pitched screw-thread 38, or, it may 40 be, multiple screw-threads. The pitch of the threads is such that the shank will rotate itself into a part into which it is driven. The bushing 20 is provided with a passage Ml therethrough which is somewhat smaller in diameter than the diameter of the screw-threads. The bushing 20 is made of material that can be scored or indented by the screw-threads. Thus by forcing the shank into the passage the screw-threads form corresponding screw-threads in the bushing so that the bushing shank can be driven in up to the head and be so firmly gripped in the bushing that it cannot become disengaged therefrom or rotate therein.

The shank preferably is relatively long so that it, has a large area in frictional engagement with the bushing. The long shank also has been found to improve the performance of the fuse since it permits the fuse link to be shortened so that there is less volume of metal vaporized when the entire length of the fuse link is vaporized upon shortcircuit. The center contact also conducts heat from the fuse link so that a link of smaller crosssectional area can be used which reduces the amount of vapors formed upon interruption.

Since the act of inserting the contact member in the passage 40 and driving it home is simultaneous the use of such contact member saves one of the operations necessary for inserting and riveting over the inner end of the usual riveted contact member. This saving in operations is important in the manufacture of a fuse where the money profit on each fuse is exceedingly small.

In the modification illustrated in Figs. 5 and 6, the shank of the center contact is more or less square in cross-section, thereby providing axially directed ribs 42 that act like the screw threads in embedding into the bushing 20.

The drop of solder :14 preferably overlies the end of the shank so that it acts as a head to prevent the contact from any harmful axial move ment in the bushing, should the contact ever become loose therein.

I claim:

A plug type electric fuse comprising a casing of frangible material having a fuse chamber therein, a button of deformable material on the bottom of said frangible casing, a center contact having a shank driven into said button and accessible within said chamber, a screw shell carried by said casing, a fusible link Within said chamber connected between said shank and said shell, solder connecting said link and shank and outstanding laterally beyond said shank and forming a head therefor.

MORRIS B. WOOD. 

